A school-based randomized controlled trial (RCT) of a gatekeeper-training program is proposed in response to the need for scientifically rigorous evaluations of interventions intended to prevent suicide. Suicide is the third leading cause of death among 15-24 years olds in the US, and rates of suicide among adolescents have increased markedly relative to the aggregate US population. R34 funding is sought for a Phase-III school level RCT of the QPR gatekeeper-training program that is embedded with the strategic prevention plan for a large district, Cobb County, Georgia. Cobb County Schools selected QPR Gatekeeper Training to implement in Fall 2003. QPR is a commonly used gatekeeper training intervention designed to enhance early detection of suicidal students and their referrals to mental health services. For this 3-year study, one-half of Cobb County middle and high schools will be randomly selected to receive QPR training of all school staff during 2003-2004. The remaining schools will be trained during 2004-2005. The accuracy and effectiveness of QPR in improving early detection of suicidal students (Aim 1) will be tested by comparing intervention and control school rates of: (a) referrals of students for suicidal behavior or ideation and follow-up assessments by mental health professionals; (b) all 15,000 8th and 10th grade students' self-reported suicidal ideation and behavior; and (c) all juvenile deaths due to suicide. To examine the impact over time of QPR on school staff members' knowledge of suicide and self-efficacy involving referral (Aim 2) we will use (a) pretest and posttest data on 8,720 staff, (b) more detailed longitudinal data from 640 staff, and (c) interviews of 60 school staff using case-cohort design. In Aims 3 and 4 we will combine these and other data to examine variation in QPR impact and individual and system level factors that lead to successful or unsuccessful integration of QPR into the schools and mental health system. This study would lead to the very first randomized trial of a gatekeeper training program, thus addressing an urgent need to identify effective programs. The designs and analytic methods would serve as a model for the rigorous evaluation of other suicide prevention programs and other low base-rate conditions.